Mask frame



FIG. 1 is a top view;

FIG. 2 is a front perspective view;

FIG. 3 is a front view;

FIG. 4 is a side view;

FIG. 5 is a rear perspective view;

FIG. 6 is a rear view; and,

FIG. 7 is a bottom view. 

The ornamental design for a mask frame, as shown and described. 